The present disclosure is related to a post-processing device that performs post-processing of a sheet-shaped printing medium such as paper onto which an image is formed by an image forming apparatus such as a copier and a printer.
In recent years, a digital multifunction peripheral (MFP) having not only a printing function but also a copying function, a facsimile function and the like is widely used as an image forming apparatus. Addition of various functions and improvements are being made to the MFP for providing increased convenience to users. An example of the functions is a paper reversing device installed in an image forming unit of the MFP for continuous printing of images (image formation) on both faces of a sheet of paper.
Basically, the paper reversing device has a paper inlet path, a feed roller pair, and a paper outlet path. The feed roller pair is composed of a reversing roller with a greater diameter and an auxiliary roller with a smaller diameter. The reversing roller and the auxiliary roller constituting the feed roller pair can rotate in forward and reverse directions while pressing against each other. The paper inlet path is directed toward between the reversing roller and the auxiliary roller and terminates at the vicinity of a contact point therebetween. An introduction opening of the paper outlet path is located close to an outer periphery of the reversing roller, not at the contact point. The paper outlet path is configured to extend in a tangential direction of the outer periphery.
In the paper reversing device thus configured, paper that is conveyed in the paper inlet path toward the feed roller pair is interposed between the reversing roller and the auxiliary roller, and then wound around the reversing roller rotating in one direction (conveyance direction). And then, when a rear end of the paper reaches a point immediately before the introduction opening of the paper outlet path, the reversing roller starts rotating in a reverse direction. The paper that is wound therearound is thus conveyed toward the paper outlet path with the rear end directed forward.
As is apparent from the above description, a top face of the paper upon introduction is directed downward upon ejection, thereby reversing the paper. The paper reversing device reverses the paper by winding the paper around the reversing roller. In such a configuration, the space occupied by the paper reversing device can be reduced and size of an entire printing apparatus can be reduced.
The paper reversing device allows continuous printing on both faces of the paper. In general, the paper onto which an image is formed by an image forming apparatus such as MFP is ejected with a printed face directed downward, in a state so-called “face-down”. However, a user may wish to eject the paper with the printed face directed upward, in a state so-called “face-up”. Face-up ejection of the paper is made possible by installing the paper reversing device in the image forming apparatus main body. Alternatively, face-up ejection of the paper is made possible also by installing the paper reversing device in a post-processing device (if any) connected to the image forming apparatus main body that performs a punching process on printed paper, a stapling process on a stack of sheets of paper, and the like.
However, installing the paper reversing device in, for example, the post-processing device only for realizing the face-up ejection, in addition to a normal face-down ejection of the paper on which an image is formed and output by the image forming apparatus, involves increased cost and increased space occupied inside the apparatus.